The present invention relates to the art of induction heating and more particularly to a method and apparatus for inductively heating the valve seats of a family of engine component configurations.
The invention is particularly applicable for heating the exhaust valve seats of internal combustion engine heads of varying configurations and will be described with reference thereto; however, it should be appreciated that the invention has broader aspects and may be used for heating a plurality of discretely spaced areas of a grouping of workpiece designs.
With the switch from leaded to unleaded gasoline, the lubricating properties of the lead compounds were removed and it was found that the exhaust seats of the engine heads were subject to increased wear at the elevated engine temperatures. To counteract the wear, it has become commonplace to inductively heat and quench harden the exhaust valve seats. Such heat treating is well suited for the automated processing required for efficient motor vehicle production. Accuracy and uniform magnetic coupling between the inductor and the valve seats are also necessary machine capabilities to provide hardness uniformity on an automated basis. It has been demonstrated that an apparatus as disclosed in U.S. Pat. No. Re. 29,046 is particularly well suited for high speed, uniform heat treating of engine valve seats. Therein, the apparatus is effective for simultaneously heating the valve seat in a single operation. This is achieved by mounting a plurality of independently reciprocable spring biased inductors on a common movable frame. At the heat treating station, the frame is moved toward the head until all the individual inductors engage the associated valve seat. The inductor coils are free to radially float with respect to the frame to compensate for manufacturing variations and are mechanically centered coaxially with the valve seat. After contacting the seats, the inductors are locked with respect to the frame, the frame is retracted a predetermined axial distance to establish a uniform magnetic coupling and the inductor coil energized to inductively heat the seats. Thus, high speed uniform heat treating is provided with dependable, non-complicated equipment.
Such an apparatus however, is basically dedicated to a single engine design, because of the design to design variations in valve seat number, spacing, orientation, size, hardness and other design parameters. While the unit could be adapted for processing other configurations, a substantial changeover time and expense is required to remove the inductors, with associated electrical, hydraulic and coolant connections, and to install inductors adapted for another configuration. In order to justify such a conversion, large volume production runs are required for each engine design. This has the effect of increasing the inventory of processed heads. Recently, the engine manufacturers have sought to reduce their inventories and obtain parts on an as required basis for all their engine requirements. Although this can be achieved by having dedicated machines, this can lead to under utilization of machines, particularly with regard to the lower volume designs.